Fair Value Measurements (Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Liabilities:
Contingent purchase price	$ 89,834		$ 96,957
Fair Value, Measurements, Recurring [Member]
Assets:
Money market	56,058		6,030
Total assets at fair value	56,058		6,030
Liabilities:
Contingent purchase price	118,571		123,757
Total liabilities at fair value	118,571		123,757
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Assets:
Money market	56,058		6,030
Total assets at fair value	56,058		6,030
Liabilities:
Contingent purchase price	0		0
Total liabilities at fair value	0		0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Money market	0		0
Total assets at fair value	0		0
Liabilities:
Contingent purchase price	0		0
Total liabilities at fair value	0		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Money market	0		0
Total assets at fair value	0		0
Liabilities:
Contingent purchase price	118,571	$ 119,612	123,757	$ 207,160	$ 369,552	$ 351,134
Total liabilities at fair value	$ 118,571		$ 123,757